Objective: Anecdotally, functional bowel disorders (FBD) such as the irritable bowel syndrome appears to cluster in some families, but no studies have investigated the heritability of FBD. We aimed to investigate the influence of heritable factors in FBD.
Methods: Same sex twin pairs enrolled in the Australian Twin Registry completed a structured interview that included questions related to symptoms consistent with FBD: abdominal pain, diarrhea, constipation, excessive gas or bloating, and nausea. Reasons for the occurrence of each symptom, including their physicians' diagnoses, were recorded. Lisrel 7.16 software was used to fit genetic models following standard procedures.
Results: Of the 686 individual twins from same-sex pairs, 33 (4.8%) had one or more symptoms diagnosed by a medical practitioner as functional bowel disorder. Complete data on this symptom scale was available for 186 monozygotic and 157 same sex dizygotic twin pairs. A model in which 56.9% (95% CI: 40.6-75.9%) of the variance was attributed to additive genetic variance, with the remaining 43.1% attributed to the individual's unique environment, closely fitted the data (chi2=0.01, df=4, p=1.0).
Conclusion: Our results suggest that a substantial proportion of the liability for FBD may be under genetic control. Whether this liability is related to the disorder itself or to other potential predisposing factors requires clarification.